'\"macro stdmacro
.\"
.\" Copyright (c) 2011 Ken McDonell.  All Rights Reserved.
.\"
.\" This program is free software; you can redistribute it and/or modify it
.\" under the terms of the GNU General Public License as published by the
.\" Free Software Foundation; either version 2 of the License, or (at your
.\" option) any later version.
.\"
.\" This program is distributed in the hope that it will be useful, but
.\" WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
.\" or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
.\" for more details.
.\"
.\"
.TH PMFAULT 3 "" "Performance Co-Pilot"
.ds xM pmfault
.SH NAME
\f3__pmFaultInject\f1,
\f3__pmFaultSummary\f1,
\f3PM_FAULT_POINT\f1,
\f3PM_FAULT_RETURN\f1,
\f3PM_FAULT_CHECK\f1,
\f3PM_FAULT_CLEAR\f1 \- Fault Injection Infrastructure for QA
.SH "C SYNOPSIS"
.ft 3
.ad l
.hy 0
#include <pcp/pmapi.h>
.br
#include <pcp/fault.h>
.sp
void __pmFaultInject(const char *\fIident\fP, int \fIclass\fP);
.br
void __pmFaultSummary(FILE *\fIf\fP);
.sp
PM_FAULT_POINT(\fIident\fP, \fIclass\fP);
.br
PM_FAULT_RETURN(\fIretvalue\fP);
.br
PM_FAULT_CHECK;
.br
PM_FAULT_CLEAR;
.sp
cc \-DPM_FAULT_INJECTION=1 ... \-lpcp_fault
.hy
.ad
.ft 1
.SH DESCRIPTION
As part of the coverage-driven changes to QA in PCP 3.6, it became
apparent that we needed someway to exercise the ``uncommon''
code paths associated with error detection and recovery.
.PP
The facilities described below provide
a basic fault injection infrastructure (for
.I libpcp
only at this stage, although the mechanism is far more general and could
easily be extended).
.PP
A special build is required to create
.I libpcp_fault
and the associated
.I <pcp/fault.h>
header file.
Once this has been done, new QA applications may be built with
.B \-DPM_FAULT_INJECTION=1
and/or existing applications can be exercised in presence of
fault injection by forcing
.I libpcp_fault
to be used in preference to
.I libpcp
as described below.
.PP
In the code to be tested,
.B __pmFaultInject
defines a fault point at which a fault of type
.I class
may be injected.
.I ident
is a string to uniquely identify the fault point across all
of the PCP source code, so something
like "libpcp/" __FILE__ ":<number>" works just fine.
The
.I ident
string also determines if a fault will be injected at run-time or not
\- refer to the
.B "RUN-TIME CONTROL"
section below.
.I class
selects a failure type, using one of the following defined
values (this list may well grow over time):
.TP
.B PM_FAULT_ALLOC
Will cause the
.B next
call to
.BR malloc (3),
.BR realloc (3)
or
.BR strdup (3)
to fail, returning NULL and setting
.I errno
to
.BR ENOMEM .
We could extend the coverage to all of the malloc-related routines,
but these three are sufficient to cover the vast majority of the uses
within
.IR libpcp .
.TP
.B PM_FAULT_CALL
Will cause the
.B next
call to an instrumented routine
to fail by returning an error code (possibly the new
.B PM_ERR_FAULT
code).
The actual error code is defined in the
.B PM_FAULT_RETURN
macro at the head of an instrumented routine.
Initially, only
.BR __pmRegisterAnon (3)
(returns
.BR PM_ERR_FAULT ),
.BR __pmGetPDU (3)
(returns
.BR PM_ERR_TIMEOUT )
and
.BR __pmAllocResult (3)
(returns
.BR NULL )
were instrumented as a proof of concept for this part of the
facility, however other routines may have this fault injection
capability added over time.
.TP
.B PM_FAULT_MISC
The ``other'' class, currently used with
.B PM_FAULT_CHECK
as described below.
.PP
To allow fault injection to co-exist within the production source
code,
.B PM_FAULT_POINT
is a macro that emits no code by default, but when
.B PM_FAULT_INJECTION
is defined this becomes a call to
.BR __pmFaultInject .
Throughout
.I libpcp
we use
.B PM_FAULT_POINT
and
.B not
.B __pmFaultInject
so that both
.I libpcp
and
.I libpcp_fault
can be built from the same source code.
.PP
Similarly, the macro
.B PM_FAULT_RETURN
emits no code unless
.B PM_FAULT_INJECTION
is defined, in which case if a fault of type
.B PM_FAULT_CALL
has been armed with
.B __pmFaultInject
then, the enclosing
routine return with the function value
.IR retvalue .
.PP
The
.B PM_FAULT_CHECK
macro returns a value that may be 0 or 1.
If
.B PM_FAULT_INJECTION
is defined then if a fault of type
.B PM_FAULT_MISC
has been armed with
.B __pmFaultInject
then the value is 1 else it is 0.
.PP
.B PM_FAULT_CHECK
is most often used in concert with the
.B PM_FAULT_POINT
macro with the
.B PM_FAULT_MISC
class to potentially arm a trigger, then test
.B PM_FAULT_CHECK
and if this has the value 1, then the
.B PM_FAULT_CLEAR
macro is used to clear any armed faults, and
the fault injection code is executed.
.PP
This is illustrated
in the example below from
.IR src/libpcp/src/exec.c :
.sp
.ft CR
.nf
    pid = fork();

    /* begin fault-injection block */
    PM_FAULT_POINT("libpcp/" __FILE__ ":4", PM_FAULT_MISC);
    if (PM_FAULT_CHECK) {
	PM_FAULT_CLEAR;
	if (pid > (pid_t)0)
	    kill(pid, SIGKILL);
	setoserror(EAGAIN);
	pid = -1;
    }
    /* end fault-injection block */
.fi
.ft
.PP
A summary of fault points seen and faults injected is produced
on stdio stream
.I f
by
.BR __pmFaultSummary .
.PP
Additional tracing (via
.B \-Dfault
or
.BR pmDebugOptions.fault )
and a new
PMAPI error code (\c
.BR PM_ERR_FAULT )
are also defined, although
these will only ever be seen or used in
.IR libpcp_fault .
If
.B pmDebugOptions.fault
is set the first time
.B __pmFaultInject
is called, then
.B __pmFaultSummary
will be called automatically to report on
.I stderr
when the application exits (via
.BR atexit (3)).
.PP
Fault injection cannot be nested.  Each call to
.B __pmFaultInject
clears any previous fault injection that has been armed, but not yet
executed.
.PP
The fault injection infrastructure is
.B not
thread-safe and should only be used with applications that are
known to be single-threaded.
.SH RUN-TIME CONTROL
By default, no fault injection is enabled at run-time, even when
.B __pmFaultInject
is called.
.PP
Faults are selectively enabled using a control file, identified by the environment
variable
.BR $PM_FAULT_CONTROL ;
if this is not set, no faults are enabled.
.PP
The control file (if it exists) is read the first time
.B __pmFaultInject
is called, and
contains lines of the form:
.ti +8n
.I ident
.I op
.I number
.br
that define fault injection guards.
.PP
.I ident
is a fault point string (as defined by a call to
.BR __pmFaultInject ,
or more usually the
.B PM_FAULT_POINT
macro).  So one needs access to the
.I libpcp
source code to determine the available
.I ident
strings and their semantics.
.PP
.I op
is one of the C-style operators
.BR >= ,
.BR > ,
.BR == ,
.BR < ,
.BR <= ,
.B !=
or
.BR %
and
.I number
is an unsigned integer.
.I op
.I number
is optional and the default is
.BR ">0"
.PP
The semantics of the fault injection guards are that each time
.B __pmFaultInject
is called for a particular
.IR ident ,
a trip count is incremented (the first
trip is 1); if the C-style expression
.I tripcount
.I op
.I number
has the
value 1 (so
.B true
for most
.IR op s,
or the remainder equals 1 for the
.B %
.IR op ),
then
a fault of the
.I class
defined for the fault point associated with
.I ident
will be armed, and executed as soon as possible.
.PP
Within the control file, blank lines are ignored and lines
beginning with # are treated as comments.
.PP
For an existing application linked with
.I libpcp
fault injection may still be used by forcing
.I libpcp_fault
to be used in the place of
.IR libpcp .
The following example shows how this might be done.
.sp
.ft CR
.nf
$ export PM_FAULT_CONTROL=/tmp/control
$ cat $PM_FAULT_CONTROL
# ok for 2 trips, then inject errors
libpcp/events.c:1  >2

$ export LD_PRELOAD=/usr/lib/libpcp_fault.so
$ pmevent -Dfault -s 3 sample.event.records
host:      localhost
samples:   3
interval:  1.00 sec
sample.event.records[fungus]: 0 event records
__pmFaultInject(libpcp/events.c:1) ntrip=1 SKIP
sample.event.records[bogus]: 2 event records
  10:46:12.413 --- event record [0] flags 0x1 (point) ---
    sample.event.param_string "fetch #0"
  10:46:12.413 --- event record [1] flags 0x1 (point) ---
    sample.event.param_string "bingo!"
__pmFaultInject(libpcp/events.c:1) ntrip=2 SKIP
sample.event.records[fungus]: 1 event records
  10:46:03.416 --- event record [0] flags 0x1 (point) ---
__pmFaultInject(libpcp/events.c:1) ntrip=3 INJECT
sample.event.records[bogus]: pmUnpackEventRecords: Cannot allocate memory
__pmFaultInject(libpcp/events.c:1) ntrip=4 INJECT
sample.event.records[fungus]: pmUnpackEventRecords: Cannot allocate memory
__pmFaultInject(libpcp/events.c:1) ntrip=5 INJECT
sample.event.records[bogus]: pmUnpackEventRecords: Cannot allocate memory
=== Fault Injection Summary Report ===
libpcp/events.c:1: guard trip>2, 5 trips, 3 faults
.fi
.ft
.SH EXAMPLES
Refer to the PCP and PCP QA source code.
.PP
The macro definitions are in
.IR src/include/pcp/fault.h .
.PP
.I src/libpcp/src/fault.c
contains all of the the underlying implementation.
.PP
.I src/libpcp_fault
and
.I src/libpcp_fault/src
contains the recipe and Makefiles for creating and
installing
.IR libpcp_fault.so
and
.IR <pcp/fault.h> .
.PP
.BR PM_FAULT_RETURN
was initiallly used in the following
.I libpcp
source files:
.IR derive_parser.y.in ,
.I pdu.c
and
.IR result.c .
.PP
.BR PM_FAULT_POINT .
was initiallly used in the following
.I libpcp
source files:
.IR derive_parser.y.in ,
.IR desc.c ,
.IR e_indom.c ,
.IR e_labels.c ,
.IR err.c ,
.IR events.c ,
.IR exec.c ,
.IR fetch.c ,
.IR help.c ,
.IR instance.c ,
.IR interp.c ,
.IR labels.c ,
.IR logmeta.c ,
.IR pmns.c ,
.I p_profile.c
and
.IR store.c .
.PP
The ``fault'' group of QA tests
show examples of control file use.  To see which tests are involved
.sp
.ft CR
.nf
$ cd qa
$ check -n -g fault
.fi
.ft
.SH DIAGNOSTICS
Some non-recoverable errors are reported on
.IR stderr .
.SH ENVIRONMENT
.TP
.B PM_FAULT_CONTROL
Full path to the fault injection control file.
.TP
.B LD_PRELOAD
Force
.I libpcp_fault
to be used in preference to
.IR libpcp .
.SH SEE ALSO
.BR PMAPI (3)

.\" control lines for scripts/man-spell
.\" +ok+ DPM_FAULT_INJECTION {from -DPM_FAULT_INJECTION}
.\" +ok+ PM_FAULT_INJECTION PM_FAULT_CONTROL
.\" +ok+ PM_FAULT_RETURN PM_FAULT_ALLOC PM_FAULT_CHECK PM_FAULT_CLEAR
.\" +ok+ PM_FAULT_POINT derive_parser PM_FAULT_CALL
.\" +ok+ PM_FAULT_MISC param_string LD_PRELOAD setoserror
.\" +ok+ initiallly {from -lpcp_fault}
.\" +ok+ p_profile tripcount __FILE__ e_labels
.\" +ok+ e_indom logmeta Dfault {from -Dfault} interp ntrip
.\" +ok+ desc pdu tmp src qa co {from co-exist} op {from op(erator)}
.\" +ok+ pmfault {man page title}
